1. Field of the Invention
The present invention relates to a hoist apparatus for raising or lowering a load along a cable and more particularly to an improved hoist apparatus which is simply constructed, relatively inexpensive and highly reliable.
2. Description of the Prior Art
The present invention is an improvement over the apparatus disclosed in U.S. Pat. No. 3,944,185 as well as all of the patents cited therein: U.S. Pat. Nos. 3,729,173; 3,721,426; 3,524,626; 3,520,515; 3,231,240; and 3,100,626. The apparatus disclosed in the 3,944,185 patent is, in brief a hoist apparatus including a motor, a power transmission, a cable driving sheave, a cable tensioning sheave, a pressure exerting chain, a diverter block, linkage and gears to transfer rotation from the tensioning sheave to a brake mechanism while at the same time allowing the tensioning sheave to pivot.
A problem has developed with this apparatus in relation to the cable becoming jammed at the diverter block after the cable has passed around the driving sheave. This occurs when the end of the cable abuts the diverter block, unravels and expands outwardly, a phenomenon commonly referred to as "bird caging". Not only is there damage to the cable, but more importantly, time is lost by an operator who must open the hoist apparatus, remove the damaged cable and then rethread the cable through the apparatus by hand. Of course while this occurs, the operator's equipment is idle and the operator is spending time on nonproductive work.
Another problem related to the accident prevention mechanism centering about the linkage and the gears. The linkage and the gears are present to transmit rotational motion from the tensioning sheave to a cam which acts as an emergency brake upon the cable. For example, if the apparatus begins to fall, the rotation of the tensioning sheave will accelerate. This acceleration is transmitted through the gears to a mechanism which actuates the cam. The gears are connected to the linkage in order to allow the tensioning sheave to pivot and yet still maintain the gears in operable contact. When the velocity of the gears suddenly increase, forces are generated which tend to rotate the linkage into an over-center position causing the gears to bind. In addition, excessive forces are also placed upon the shafts on which the gears are mounted, again causing binding. Once again, these problems necessitated the time of an operator to correct as well as time for replacing any damaged parts.
Further problems have also been noticed which have detracted from the effective operation of the hoist.